Various types of memory devices are known in the art for storing data used by various kinds of computing devices. Generally, memories include elements that can take one of two or more states wherein each state corresponds to a logical element used by an associated computing device. For example, many memory devices include elements that can be maintained in two states, one corresponding to a logic “zero” and a second corresponding to a logic “one.” One example of a known memory device is a ferroelectric memory, also known as ferroelectric random access memory (FRAM or FeRAM). In a ferroelectric memory device, the element that can assume two states is a ferroelectric capacitor.
A ferroelectric capacitor, when biased with a voltage, maintains an electric potential when the bias voltage is removed. The ferroelectric capacitor can maintain this electric potential without application of an outside power source. So configured, a ferroelectric device based memory can maintain its stored state in the absence of the application of electricity, thereby making it a low-power option for a memory device. When a ferroelectric memory device is read, however, the state of the ferroelectric device is erased. To maintain the previous state, the ferroelectric element must be rewritten with the previous state after reading. This rewrite process can delay a cycle time for a ferroelectric device, thereby decreasing the speed at which ferroelectric memory device can operate. Moreover, it may be necessary to clear charge from a ferroelectric memory bit cell either at the end of a read cycle or at the beginning of a new read cycle. Clearing charge from the ferroelectric memory device can further delay the cycle time, which further degrades the speed performance for the memory device.
In certain known FRAM devices, an isolator switch is placed between the ferroelectric capacitor and the sense amplifier to allow fast sense amplifier setting and signal amplification because of the resistive decoupling of the sense amplifier from the ferroelectric capacitor elements provided by the isolator switch. The isolator switch, however, prevents automatic write back of data to the ferroelectric capacitor by the sense amplifier. To write a state back onto the ferroelectric capacitor in FRAMs using an isolator switch, the data signal needed to be boosted significantly, and the sense amplifier 650 needed extra time to sink or source charge needed for write back.